This invention relates to methods and arrangements for the interruption of current in direct current (DC) circuits. This invention may also provide advantages for alternating current circuits as well.
The interruption of a DC circuit containing inductance requires the inductive energy stored in the circuit to be dissipated by or stored within the circuit breaker. Many circuit breaker designs dissipate the energy stored in the circuit upon circuit interruption by increasing the circuit resistance through various techniques during interruption. As the resistance is increased, the system current is decreased until it reaches zero and the interruption is complete.
Related prior art utilizes conventional mechanical contacts in the circuit path as the circuit interruption devices and provides mechanical or electronic switches (i.e., liquid metal cathode switch tubes, crossed field switch tubes, and the like) as commutation switches to successively introduce increased resistance to absorb the circuit energy subsequent to opening a circuit interruption device. The Lian Patent No. Re 27,557 discloses a mechanical circuit interrupter shunted by a commutation circuit of resistors and switches which are normally closed. Upon circuit interruption, the in-line mechanical contacts are opened to divert current into the commutation circuit, and subsequently, the commutation switches are successively opened to increase shunt resistance so that, when the last switch is opened, the remaining circuit energy can be absorbed in a surge suppressing resistance-capacitor circuit. This and other related prior art such as the Lutz et al. U.S. Pat. No. 3,660,723; the Lian et al. U.S. Pat. No. 3,641,358; the K. T. Lian U.S. Pat. No. 3,534,226; the Lutz U.S. Pat. No. 3,611,031; and the like are suited for high voltage DC power transmission. However, such arrangements incur the shortcomings of in-line mechanical switches such as slow interruption time, shock sensitivity, arcing, contact burning, and noise due to the mechanical nature of the switching devices.